The resistance of mouse neuroblastoma membranes to lipid peroxidation is determined by the culture conditions. This phenomenon has been related to the antioxidant activity of the neuroblastoma neutral lipid fraction using a recently developed assay. Fractionation of neutral lipid samples on LH-20 Sephadex and subsequent studies employing gas chromatography and mass spectrometry have led to the isolation and partial characterization of a highly aromatic, phenolic antioxidant having a molecular weight of 274 amu. This antioxidant will be further characterized by NMR studies and by synthesis. On the basis of this information, specific, inexpensive assay for this compound will be devised. This assay will be used to investigate the biological role of the antioxidant.